Sturgeons in a pond - Micro-guide by Foudebassin experts

The genus Acipenser includes 17 species including Acipenser sturio commonly called "sturio", "European sturgeon", "Baltic sturgeon", "Gironde sturgeon" or "common sturgeon". But this last name no longer suits this ancestral fish threatened, in the short term, with complete extinction...

An archaic appearance The sturgeon, which can reach 4 m in length, is distinguished from other fish by its elongated shape, its body devoid of scales, and its poorly ossified skeleton. It is also characterized by a relatively long and pointed rostrum, a protractile ventral mouth but devoid of teeth, a widely split lower lip, four short sensory barbels and an asymmetrical caudal fin giving it, somewhat, the appearance of a shark.

Instead of scales , it has 5 rows of large bony shields (or scutes) 1 on the back, 2 on the sides and 2 on the belly. The olive-grey back of the European sturgeon resembles that of the Russian sturgeon but is distinguished from the brown-black back of the starry sturgeon. Its belly is white, its fins are brownish and its scutes are whitish. Small fish will become… migratory Like other sturgeons, with the exception of the sterlet which does not join the marine environment, the sturio is a migratory potamotoque fish (which spawns in fresh water). The adult European sturgeon lives most of its life in the ocean.

In the spring, during the migrating period, the spawners leave the sea waters, stop feeding and go up the river to reproduce. (The sexual maturation of the male sturgeon is around 10 years old and that of the female sturgeon around 15 years old). Between May and July, the female lays on a gravel substrate between 12,000 and 34,000 oocytes per kilo of her weight. These eggs, deposited in a place where the current is strong, drift and then adhere to the pebbles and rocks.

The incubation period varies according to the water temperature: it is between 56 and 108 degree-days. For 1 to 2 months, the fry, which remain close to their place of birth, feed almost exclusively on chironomid larvae. Then, the juvenile fish, in search of more plentiful food, go down the river to reach the brackish waters of the estuary. (Until 1982, when sturgeon fishing was banned, this was the time when the sturio was most vulnerable). From this moment on, the fish makes many river-estuary-sea movements. The adult fish, which has reached a size of about 60 cm, begins its descent towards the sea by making seasonal migrations between the upper and lower estuaries.

When it reaches the sea waters, it reaches the sandy bottoms at a depth of between 20 and 80 m without straying too far from the coast. It continues to feed on benthic invertebrates or small fish… A fish seriously threatened with extinction The sturio is found in the Black Sea, in the Atlantic (from Norway to Spain) and on the northern and eastern coasts of the Mediterranean.

Quite common on all the coasts and rivers of Western Europe at the end of the last century, its population has declined sharply since the intensification of fishing at sea and in estuaries for the exploitation of caviar (in 1945 in the Garonne 20 tonnes of females were caught), the construction of dams, the deterioration of water quality, the destruction of spawning grounds for the extraction of gravel.

Despite a serious repopulation programme, the sturgeon - which can live to be a hundred years old - remains among the fish seriously threatened with extinction and it will probably take 20 to 30 years of combined international efforts for the species to no longer appear on this red list.